Making a mark: how to keep track of components

A variety of component marking techniques – to suit all applications and budgets – help manufacturers achieve everything from product branding through to production tracking and part traceability.

In today’s fast-moving manufacturing environment, component marking is critical. Modern marking systems are often fully automated and integrated within production lines and ERP systems to provide complete product traceability – from the point of manufacture all the way through to point of use.

Automation has increased the speed and complexity of manufacturing and this has to be mirrored in component tracking.

Individual parts are made at high speed, which must then be assembled quickly and precisely. By marking each component with a unique identity, this can be scanned prior to each operation and tracked efficiently through production.

This is also used beyond the production process: accurate traceability also helps to ensure that replacement parts are speedily replaced, for instance, or that a rogue batch can be recalled quickly.

Components can be marked in various ways, from a simple serial number to a scannable barcode.

There are several ways to achieve this, ranging in effectiveness, budget and complexity, with each method having its relative advantages and disadvantages in different applications. For example, laser marking is a fast, effective way to mark a range of components, while chemical etching, scribing and dot peening (also known variously as dot marking, stylus pin marking and micro-percussion marking) are some of the other major techniques.

Laser focus

Laser marking has three main variants: CO2, YAG and Fibre. CO2 lasers have a relatively long wavelength, making them a poor choice for metal marking. YAG and Fibre lasers use shorter wavelengths that are easily absorbed by metal – and provide better marking resolution.

The light source of Fibre lasers is sealed, to prevent dust and particle contamination. This enables longer distances between the control unit and marking head, which is vital in some production line applications. It also reduces leakage, to boost efficiency. YAG systems are usually for specialist applications – especially in the scientific sphere – while Fibre lasers are more commonly used in the industrial sector.

Laser marking has become commonplace in medical applications, especially since the advent of Unique Device Identification (UDI) legislation. Here, laser marking can make a permanent, high contrast mark that lasts for the lifetime of the product, while simultaneously being smooth and resistant to sterilisation.

Although laser marking has enormous benefits, it will be too expensive and complex for many applications – meaning that manufacturers must offer a range of other options to choose from.

Alternative methods

Chemical etching (also called electrochemical or electrolytic etching) uses an electric current to mark alphanumeric data or Data Matrix codes onto metal surfaces. It is common for small to medium production runs in the aerospace industry, which has tight tolerances over surface treatment. A stencil of the design to be marked is placed between the electrode and the surface, and a low voltage current passed through an electrolyte to etch the material. It does not deform the material being marked, which is important in applications ranging from small pipes and shims to feeler gauges.

In scribe marking, a pneumatically actuated pin is driven into the metal surface then moved through the metal to engrave an inscription in a continuous line.

In this method, the work piece must be held firmly, or there is little chance of making a good quality mark. Scribe machines need firm fixturing because they generate high lateral forces during operation. Deeper marks are harder to make than light ones, and this is influenced by factors including marking force, and both the radius and angle of the tip.

Marking force is controlled by adjusting pneumatic pressure. This is usually set to 45 psi but should not be turned up too high. The tip may stick in the material, causing the machine to stall, although this can be solved by reducing either the air pressure or marking speed.

The tip radius usually varies between 0.5mm and 1mm. Smaller radii give deeper marks, but can tear the material, instead of forming it. The standard tip angle is 110°, although this can be modified for special applications.

On the dot

Finally, dot peening uses a stylus to indent a series of dots on a material surface. The stylus is programmed to move across the surface and create characters, logos or a Data Matrix code – a kind of ‘barcode’ that stores large amounts of data.

Dot peen marking is fast and accurate and can mark through coatings or film on a material’s surface. It is particularly useful for permanently marking a Data Matrix code onto metal components.

When using dot peening, the depth of the mark – which is a measure of legibility – depends on factors such as marking force, marking gap (the distance from the stylus tip to the workpiece), material hardness and angle of the stylus tip.

A larger marking gap creates a deeper mark. However, if the gap is too large then the stylus will start to stick and drag the workpiece. This is solved by reducing the gap or increasing the marking force. While the stylus tip angle is usually set at 90°, it can either be reduced or increased. A wider angle (such as 120°) will make a shallower mark, but lengthen the life of the stylus. On the other hand, a smaller angle (say 60°) will make a deeper mark while reducing stylus life.

Dot peening machines can mark characters from 0.15 to 49.95mm (0.006 to 1.967in) high. Very large or very small characters should be avoided if possible. Small characters are generally up to 1.00mm (0.040in), medium characters are 1.00 to 4.00mm (0.040 to 0.160in) and large characters are above 4.00mm (0.160in).

Surfaces do not have to be completely flat, but if they are not then the depth of the mark will vary across the surface. For dot marking, as the marking gap increases, so will the depth of the mark. If the difference in gap is only 1-2 mm (0.040 to 0.080in), the mark made should be acceptable.

If marking a very contoured surface – such as a cylindrical work piece – there are several points to consider:

Use as large a gap as possible: if the initial gap is 5mm (0.200in), then a change of 1mm (0.040in) will have less effect than if the initial gap had been 2mm (0.080in), for instance;

Mark a line of text by splitting it into several sections, then marking each with a different force – to compensate for the change in gap. With this approach, a Split Line software function will assist if marking variable data; and,

Reduce the character size or width so that the whole mark is shorter.

There are many reasons for carrying out product marking – ranging from simple identification (such as adding a company logo) to production line tracking. The wide range of available options ensures that all types of capability – and budget – are catered for.

This article features in industry magazine Production Engineering Solutions, read the full article here